ISPConfig3 and Checking Email?

I am wondering if there is docs or information on how to check email with an ISPConfig 3 server? I am used to ISPConfig 2 with the web#_username and all defaulting to the primary domain. I am receiving email fine as they are showing up in the vmail directory under each email. But when I check email using thunderbird, it doesn't recognize username/password. Any help would be great!!!